Audio Scrambler and Sub-Audio Signalling Processor
CMX138A
The detailed descriptions of the C-BUS registers are presented in numerical order and should be read in
conjunction with the relevant functional descriptions.
9.1.1 Reset Operations
A reset is automatically performed when power is applied to the CMX138A. A reset can be issued as a C-
BUS command, either as a General Reset command ($01), or by setting the appropriate bit (b5) in the
Powerdown Control register ($C0). In the latter case, an option exists to protect the values held in the
Program Block (which is accessed via the Programming register, $C8). The action of each reset type is
shown in the table below:
Table 8 Reset Operations
Protect bit
($C0 b4) state
Program
Block state
Reset type
1 Power On
cleared by h/w default
cleared by h/w default
General Reset
2
(C-BUS $01)
Reset
(C-BUS $C0 b5)
Reset
(C-BUS $C0 b5)
3
0
1
default
4
protected
Following a Reset operation, the internal checksum values are made available in the $AA, $B8 and $B9
registers. The device ID is available in $C5.
The status of the Power-Down register, $C0, can be read back in $C4 to ensure that C-BUS
communications are operational.
9.1.2 General Reset - $01 write
The General Reset command has no data attached to it. It puts the device registers into the states listed
below. A power-on reset performs the same action.
© 2010 CML Microsystems Plc
Page 38
D/138A/2
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